1 Technical Field
The present invention relates to rotating electric machines which include at least one multi-phase coil, at least one armature core and a plurality of magnetic poles.
2 Description of Related Art
To achieve a small size, high performance, long service life and high reliability, rotating electric machines generally employ a brushless structure with a permanent magnet field. On the other hand, for usage in a wide rotational speed range, it is necessary to vary the field strength. However, with the aforementioned permanent magnet field, it is difficult to vary the field strength; thus losses occur and there are limits on the characteristics of the rotating electric machines. Therefore, one may consider employing a winding field instead of the permanent magnet field. However, the space required for receiving a winding is generally larger than that required for receiving a permanent magnet. Moreover, a winding is generally required to be surrounded by a core. Consequently, a considerably large volume is required for employing the winding field. As a result, it is difficult to achieve the original object, i.e., to achieve a small size and high permeance.
Japanese Patent Application Publication No. JP2013212037A discloses a hybrid excitation rotating electric machine that has an exciting coil arranged in a suitable position, thereby forming a desired magnetic circuit without increasing the size of the rotating electric machine; the exciting coil functions to excite magnetic poles that are not magnetized by permanent magnets. More specifically, the hybrid excitation rotating electric machine includes: a rotor having first and second rotor cores; a stator that generates a rotating magnetic field for rotating the rotor; and the exciting coil that protrudes radially inward from the stator so as to be arranged in a gap formed between the first and second rotor cores.
However, with the above configuration of the hybrid excitation rotating electric machine, the number of the rotor cores is equal to 2, thus increasing the parts count and size of the rotating electric machine. Moreover, the magnetomotive force of the exciting coil acts in a direction of weakening the magnetomotive forces of permanent-magnet magnetic poles. Consequently, when electric current supplied to the exciting coil is increased for the purpose of increasing the output of the rotating electric machine, the potentials of permanent magnets are suppressed.